1. Field of the Invention
The present invention relates to an apparatus for producing filaments from meltable material utilizing centrifugal force.
2. Description of Related Art
An apparatus of this kind has been disclosed by U.S. Pat. No. 3,596,312. It consists of a cylindrical hollow body open at the top, rotating at high speed about its vertical axis. It is surrounded peripherally by a wall in the form of a cylindrical casing, which has a plurality of discharge openings. Concentrically with this cylindrical wall, the rotating hollow body contains a heating device which is capable of melting, upon contact, the meltable synthetic material that is introduced into the hollow body in a solid condition. The heating device rotates at the same speed as the rest of the hollow body about its rotation axis.
The known apparatus further contains a funnel-shaped charging station through which the solid synthetic material continuously falls by gravity into the rotating hollow body, strikes its bottom, and is thrown toward the heating device by centrifugal force. From there, again because of the centrifugal force acting on it, it is delivered over a short distance to the outer cylindrical casing provided with openings, thrown out through these openings, and cooled in filament form. Rotation of the cylinder is effected by a drive device, for example an electric motor.
According to one alternative, the material to be melted is charged into the rotating cylindrical cavity in the form of pellets, flakes, or powder. Thermoplastics, such as polyamide, polyethylene, polystyrene, and polypropylene, are mentioned as suitable synthetic meltable materials.
The spherical or cylindrical heating device in the interior of the rotating hollow body is operated electrically. The hollow body is closed; i.e. its entire internal volume is used for heating.
The material leaving the rotating hollow body through the peripheral nozzle openings is, while it is immediately cooled into individual fibers, continuously pulled downward into a bell-shaped stationary suction device surrounding the rotating hollow body at a distance, and can thus be immediately coiled up as a twisted, endless fiber yarn. The length of the resulting monofilaments can be influenced by varying the temperature of the molten polymer material and the rotation speed of the hollow body.
The particular centrifugal force acting on the polymer is determined by the rotation speed and/or the internal radius of the hollow body.
The advantage of this kind of apparatus and of the method indicated lies especially in the complete utilization of the meltable fiber-forming material that is used. Drawing into fibers or filaments occurs essentially by means of centrifugal force, and can be very precisely controlled thereby.
A disadvantage of this known apparatus, however, is that the thermoplastic polymer material melted by the heating device must, in the hot, fluid state, cover a certain distance tangential to the rotation direction of the hollow body in order to reach the discharge openings of the rotating outer cylindrical casing which are arranged concentrically with the heating system. The time period in which this distance can be covered is not less than three seconds. The result of this is that with thermoplastic polymers which decompose easily--e.g. in cases where the decomposition temperature is just above the softening temperature--pyrolysis will begin during this period of time, and for that reason, and because the nozzles become clogged with pyrolyzed material, fiber formation is disrupted or made entirely impossible.
Examples of such problematic thermoplastic fiber-forming materials are polyesters and polyamides that are not predried and still contain more than 50 ppm water, for example polybutylene terephthalate, polyethylene terephthalate, and polyepsilon caprolactone, as well as the easily pyrolyzed thermoplastic materials ethylene vinyl acetate, polyurethane, polyester polyurethane, the polylactides, and polyhydroxybutyrate/polyhydroxyvalerate copolymers, as well as native sugar, for example sucrose.